Method of making cast movable joint



March 25, 1969 PROSEN 3,434,526

METHOD OF MAKING CAST MOVABLE JOINT Original Filed Sept. 6. 1960 INVENTOR EMIL M. PROSEN AIIQRNE Y5.

3,434,526 METHOD OF MAKING CAST MOVABLE JOINT Emil M. Prosen,Bala-Cynwyd, Pa., assignor to Nobilium Products, Inc, Philadelphia, Pa.,a corporation of Pennsylvania Continuation of application Ser. No.54,229, Sept. 6, 1960. This application Mar. 15, 1965, Ser. No. 444,900lint. Cl. B22d 31/00, 23/06; B22c 9/12 US. Cl. 164-69 3 Claims Thisapplication is a continuation of my pending ap plication, Ser. No.54,229, filed Sept. 6, 1960 (now abandoned) and relates to castarticulated assemblies or movable joints for use in prostheticdentistry, and to the method of making the same.

In accordance with current practice in prosthetic dentistry where claspson a dental restoration are provided for engagement over natural teethto hold the re storation in place in the mouth of a wearer, the claspsare rigidly held by the restoration and are immovably held on thenatural teeth and as a concomitant thereof the clasps must move withmovement of the restoration during mastication. Such movement imposes asevere strain on the teeth over which the clasps are applied and causesfrequently, not only discomfort to the wearer of the restoration butalso loosening of the clasped teeth. Although numerous attempts havebeen made to remedy the aforementioned shortcoming in mounting clasps ofdental restorations, so far as I am aware none of the structuresproposed and applied to noble metals and high melting point alloys usedin dental restorations have proven satisfactory.

Accordingly, it is an object of the present invention to provide a castarticulated assembly or movable joint for use in prosthetic dentistry,wherein limited movement in all directions is provided between the partsat the joint.

A more specific object of the invention is to provide a dentalrestoration comprising a cast metal support with tooth clasps, whichrestoration is capable of independent limited movement or play in alldirections relative to the clasps.

A further object of the invention is to provide a novel method ofprocedure in forming tooth clasps on cast metal dental restorationswhereby the metal support for the clasps will be capable of limitedmovement in all directions in relation to the clasps.

The foregoing and other objects of the invention, not specificallyenumerated, I accomplish by forming one of the members of the castmovable joint with a projection which is to be engaged within a socketin the other member of the cast metal joint, then applying to theprojection a coating composition to a thickness corresponding to theamount of freedom of movement desired in the joint between the members;then applying said coated cast member on a refractory model after whichsaid model and said first mentioned member are fully waxed and investedand the wax then melted out to provide a mould within which a casting ismade in the usual manner. Such casting consisting of both members infirm engagement is then removed from the mould. The casting is thentreated to dissolve away the coating composition, thus leaving the firstand second members of the joint in assembled relation with the desiredfreedom of movement or play therebetween. The invention will be betterunderstood from the detailed description which follows when consideredin connection with the acompanying drawing wherein:

FIG. 1 is a top plan view of a dental restoration embodying theinvention, shown in relation to natural teeth over which the restorationis to be removably anchored, the restored teeth being omitted from therestoration.

FIG. 2 is a section taken along the line 2-2 of FIG. 1.

nited States Patent FIG. 3 is a section taken along the line 3-3 of FIG.2.

FIG. 4 is a section of a preformed clasp member having a soluble heatrefractory coating applied to a portion thereof prior to having thesupporting part of the restoration cast around the coated portion of theclasp.

In the drawing wherein I have shown my invention applied to a dentalrestoration for the lower jaw of a human mouth, the reference character10 indicates natural teeth, shown in phantom, in relation to which adental restoration 11 is applied. The restoration, which is merelyillustrative consists of a pair of saddle members 12 having artificialteeth (not shown) mounted thereon, the saddles being supportable on thelower alveolar ridge and joined together by a lingual connecting bar 13,each saddle having floatingly mounted therein a tooth clasp 14 having aplurality of prongs 14a, 14b and engageable over a second premolar tohold the restoration in place.

According to the present invention the clasps on the saddles are such asto provide for limited relative movement or play in all direction of thesaddles relative to the clasps so that during mastication the slightmovements of the saddles will not be transmitted to the clasps and as aconcomitant thereof impose stresses on the teeth upon which the claspsare anchored. To this end provision is made for limited spatial movementor play in all directions for the saddles relative to the clasps. Thisis accomplished by forming the clasps and saddles with interengagedsubstantially complementary non-removable parts 16 and sockets 17respectively, part 16 being a hook-shaped projection on the claspsimilar in form and of somewhat smaller size in all dimensions than thesocket 17 in the saddle.

To provide the desired freedom of movement of the saddles relatively tothe clasps, each clasp 14 consisting of the prongs 14a, 14b, 14c and thehook-shaped projection 16 is preformed in wax on a refractory model ofthe toothed jaw, and is then cast by the Well-known lost wax procedure.The hook-shaped projections 16 of the cast clasps are then coated with achemically soluble high heatresistant refractory substance 18 to athickness corresponding to the extent of movement desired between thesaddles and the clasps. The coating may be either a fritlike coatingsubstance or a metal deposit formed by electro-plating. A suitablefrit-like coating substance has the following composition: water 81000., sodium silicate 945 cc., wetting agent 2.5 cc., silica flour 1300gr., zirconium silicate 2300 gr., chromic oxide 20 gr. The fritlikecomposition may be painted onto or otherwise applied to the projectionsand caused to set thereon by being subjected to a temperature ofapproximately 1400 F. Where the coating is a metal applied byelectro-plating, it is preferable that said metal be nickel which can bedissolved away by an acid which will not attack the noble metals or thenon-precious metal alloys used in making dental restorations.

The clasps as thus coated are placed on a refractory model which is areproduction of the original model and the model is then fully waxed toprovide for the entire metal casting required for the saddles 12, theconnecting bar 13, and the coated projections 16 of the clasps. Thewaxed-up model is then invested with a refractory case and the Wax thenmelted out to provide a mould space in which the casting is made in theusual manner. The casting which is in firm engagement with theprojections on the preformed clasps is then removed from the case,cleaned of the refractory material and the sprues cut away.

To remove the heat refractory frit-like coating from the claspprojections which are embedded in the composite casting, said casting istreated in boiling sodium hydroxide for about 30 minutes to dissolve thecoating,

thus providing the limited space or socket within the saddles to permitrelative movement between said saddles and clasps. As some sodiumhydroxide may remain and solidify at room temperature within the spacethus provided between the projections on the clasps and saddles suchremaining sodium hydroxide may be removed by treating the casting in a50% nitric acid solution and the casting then rinsed with water.

If nickel plating is employed to provide the heat refractory coating onthe projections of the clasps, such coating can be removed by treatingthe casting in hot nitric acid until all of the deposited nickel isdissolved away to provide the sockets within the saddles around theprojections on the clasps.

After the clasps are mounted in the saddles to provide the freedom ofmovement between said parts, the dental restoration may be finished in amanner Well understood by a dental mechanic.

Although I have shown and described a preferred embodiment of myinvention as applied to a dental restoration having two saddles, twoclasps and a connecting bar between the saddles, it will be understoodthat the technique described could be employed in breaking the rigidityin the structure of a dental appliance, for example intermediate or atthe ends of a connecting bar. Accordingly, the foregoing description anddrawing are to be considered as exemplary and not in a limiting senseand is to be construed within the scope of the appended claims.

What I claim is:

1. The method of forming a removable dental restoration having a toothclasp and a supporting part for the clasp, in which restoration thesupporting part has a socket therein and the clasp has a projection of ashape similar to, smaller than and engaged non-removably in said socketso as to a provide for limited free play movement of the supporting partin all directions relative to said projection, said method comprisingfirst preforming a casting by the lost wax technique of the clasp andits projection from a wax-up of the clasp and its projection on arefractory model, coating the projection on the clasp with a chemicallysoluble high heat-resistant refractory substance to a thicknesscorresponding to the extent of movement desired for the supporting partrelatively to the clasp, firing said refractory substance, mounting thecast coated clasp on the aforementioned refractory model, forming awax-up of the supporting part around the coated projection investing theresulting model, melting out the wax to provide a mould, casting thesupporting part around the coated projection on the clasp, removing thecasting from the mould and dissolving away the refractory coatingsubstance to provide a pocket clearance in said casting corresponding tothe thickness of said heat-resistant refractory coating.

2. The method according to claim 1 wherein the coating substance is afrit-like composition which after firing is soluble in boiling alkali.

3. The method of forming a removable dental restoration having a toothclasp and a supporting part for the clasp, in which restoration thesupporting part has a socket therein and the clasp has a projection of ashape similar to, smaller than and engaged nonrernovably in said socketso as to provide for limited free play movement of the supporting partin all directions relative to said projection, said method comprisingfirst preforming a casting by the lost wax technique of the clasp andits projection from a Wax-up of the clasp and its projection on arefractory model, coating the projection on the clasp with a chemicallysoluble high heat-resistant refractory substance to a thicknesscorresponding to the extent of movement desired for the supporting partrelatively to the clasp, mounting the cast coated clasp on theaforementioned refractory model, forming a wax-up of the supporting partaround the casted projection investing the resulting model, melting outthe wax to provide a mould, casting the supporting part around thecoated projection on the clasp, removing the casting from the mould anddissolving away the refractory coating substance to provide a pocketclearance in said casting corresponding to the thickness of saidheat-resistant refractory coating, and wherein the coating substance isa metal plating which is soluble in a reagent which is non-reactive tothe metals forming the clasp and the supporting member.

References Cited UNITED STATES PATENTS 2,546,397 3/1951 Johnson.

2,550,436 4/1951 Yates 32--7 1,657,476 1/1928 Inami 22190.1 2,042,3305/1936 Bradley 22-190.1 2,196,505 4/ 1940 Morton 32-6 2,227,735 1/ 1941Morton 326 2,797,482 7/1957 Zahn 325 2,628,166 2/1953 Haller l6490 X J.SPENCER OVERHOLSER, Primary Examiner.

V. K. RISING, Assistant Examiner.

US. Cl. X.R. 327; 16412, 90, 36, 111; 24954, 98, 61; 10638.3

1. THE METHOD OF FORMING A REMOVABLE DENTAL RESTORATION HAVING A TOOTHCLASP AND A SUPPORTING PART FOR THE CLASP, IN WHICH RESTORATION THESUPPORTING PART HAS A SOCKET THEREIN AND THE CLASP HAS A PROJECTION OF ASHAPE SIMILAR TO, SMALLER THAN AND ENGAGED NON-REMOVABLY IN SAID SOCKETSO AS TO A PROVIDE FOR LIMITED FREE PLAY MOVEMENT OF THE SUPPORTING PARTIN ALL DIRECTIONS RELATIVE TO SAID PROJECTION, SAID METHOD COMPRISINGFIRST PREFORMING A CASTING BY THE LOST WAX TECHNIQUE OF THE CLASP ANDITS PROJECTION FROM A WAX-UP OF THE CLASP AND ITS PROJECTION ON AREFRACTORY MODEL, COATING THE PROJECTION ON THE CLASP WITH A CHEMICALLYSOLUBLE HIGH HEAT-RESISTANT REFRACTORY SUBSTANCE TO A THICKNESSCORRESPONDING TO THE EXTENT OF MOVEMENT DESIRED FOR THE SUPPORTING PARTRELATIVELY TO THE CLASP, FIRING SAID REFRACTORY SUBSTANCE, MOUNTING THECASE COATED CLASP ON THE AFOREMENTIONED REFRACTORY MODEL, FORMING AWAX-UP OF THE SUPPORTING PART AROUND THE COATED PROJECTION INVESTING THERESULTING MODEL, MELTING OUT THE WAX TO PROVIDE A MOULD, CASTING THESUPPORTING PART AROUND THE COATED PROJECTION ON THE CLASP, REMOVING THECASTING FROM THE MOULD AND DISSOLVING AWAY THE REFRACTORY COATINGSUBSTANCE TO PROVIDE A POCKET CLEARANCE IN SAID CASTING CORRESPONDING TOTHE THICKNESS OF SAID HEAT-RESISTANT REFRACTORY COATING.